1. Field of the Invention
The present invention to a method for fabricating semiconductor devices, and more particularly, to a method for forming metal lines, which can form metal lines in a polymer dielectric film without deterioration of buried metal resulting from damage of the polymer dielectric film.
2. Description of the Prior Art
In the high-integrated semiconductor devices, several characteristics, such as a resistance characteristic etc., have been pointed out to be a big problem. Thus, in the process of integrating metal lines having a low dielectric film and a low resistance, a technical development has been studied. Here, for the low dielectric film, a ploymer material having a composition adding oxygen to a compound of carbon and hydrogen is used. For the metal lines, metal material such as tungsten (W), aluminum (Al) or copper (Cu) is used.
FIGS. 1A through 1C are sectional views illustrating a conventional method for forming metal lines.
The conventional method for forming metal lines first prepares a semiconductor substrate 1 with a lower metal line 2 as shown in FIG. 1A. Then, a polymer dielectric film 3 and an oxide film 4 are successively formed on the semiconductor substrate 1. A photosensitive film is coated on the oxide film 4 and exposure and development are performed to the photosensitive film, thereby forming a photosensitive film pattern 9 which partially exposes the lower metal line 2.
Then, as shown in FIG. 1B, the photosensitive film pattern is used as a mask to perform dry etching to the oxide film and the polymer dielectric film, thereby forming a contact h1 which partially expose the lower metal line 2. Then, the photosensitive film pattern is removed.
In dry etching, a metal oxide film 5 is formed on a surface portion of the lower metal line which is exposed via the contact h1. In a subsequent process step, the metal oxide film 5 functions to prevent the lower metal line from being electrically connected with an upper metal line. Therefore, after dry etching, RF sputter etching is performed to remove the metal oxide film. RF sputter etching uses Ar ions which simultaneously etch lateral and upper portions of the contact with kinetic energy.
Then, as shown in FIG. 1C, a wetting Titanium (Ti) film (not shown) and an Aluminum (Al) film (not shown) are successively deposited on an upper face of the contact h1 thereby forming an upper metal line 6 which is electrically connected with the lower metal line 2 as shown in FIG. 1C. The Ti film functions as a ground film.
FIG. 2 is an SEM photograph illustrating a problem in the prior art.
In the prior art, the polymer dielectric film is damaged during RF sputter etching unlike a typical silicon oxide film, thereby increasing the surface coarseness within the contact. Where the upper metal line is formed on the polymer dielectric film, the surface coarseness of the metal film also increases in response to the surface coarseness of the polymer dielectric film.
In particular, when the metal film for the upper metal line is embedded in the contact, it is most important to form a uniform and continuous metal film at an initial stage so as to readily embed a subsequently deposited metal film. However, where the surface coarseness of the metal film is increased as above, the metal film is discontinuously deposited at the initial stage causing a process step of embedding the metal film to be difficult.